Lubricating oils with enhanced piston deposit control capability

ABSTRACT

The lubricant composition of the present disclosure comprises a major amount of a base oil and a minor amount of an additive composition comprising an overbased detergent and a low-base detergent, wherein the lubricant composition has a salt to metal ratio ranging from about 3.0 to about 8.0.

DESCRIPTION OF THE DISCLOSURE

1. Field of the Disclosure

The present disclosure relates to a lubricant composition, its method of preparation and use. More particularly, the present disclosure relates to a lubricant composition comprising an overbased detergent and a low-base detergent.

2. Background of the Disclosure

Lubricating oils that are suitable for use in modern engines must meet industry performance specifications, such as ILSAC GF-4 and API SM. One of the requirements of ILSAC GF-4 and API SM is to pass the Sequence IIIG test. The Sequence IIIG test measures oil thickening and piston deposits during high temperature conditions. In order to meet the minimum standard for GF-4/SM, the test oil has to give Sequence IIIG viscosity increase at 150% maximum and weighted piston deposit (WPD) at 3.5 minimum. However, certain OEMs have demanded higher performance levels for their specific family of engines as stipulated in their internal specifications. For example, General Motors GM4718M requires the Sequence IIIG viscosity increase at 90% maximum and WPD at 5.5 minimum.

Accordingly, there is a need for a lubricant composition that can meet the higher performance levels as required by the new generation of engines. The present disclosure proposes a lubricant composition that can have at least one of enhanced piston deposit control capability and viscosity control.

SUMMARY

In accordance with the disclosure, there is a lubricant composition comprising a major amount of a base oil and a minor amount of an additive composition comprising an overbased detergent and a low-base detergent, wherein the lubricant composition has a salt to metal ratio ranging from about 3.0 to about 8.0.

According to another embodiment of the present teachings, there is a method of improving piston cleanliness comprising providing to at least one piston a lubricant composition comprising a major amount of a base oil and a minor amount of an additive composition comprising an overbased detergent and a low-base detergent, wherein the lubricant composition has a salt to metal ratio ranging from about 3.0 to about 8.0.

According to yet another embodiment of the present teachings, there is a method of passing a Sequence IIIG test in a combustion system comprising providing to the combustion system a lubricant composition comprising a major amount of a base oil and a minor amount of an additive composition comprising an overbased detergent and a low-base detergent, wherein the lubricant composition has a salt to metal ratio ranging from about 3.0 to about 8.0.

According another embodiment of the present teachings, there is a method of lubricating moving parts of a machine, said method comprising contacting at least one moving part with a lubricant composition comprising a major amount of a base oil and a minor amount of an additive composition comprising an overbased detergent and a low-base detergent, wherein the lubricant composition has a salt to metal ratio ranging from about 3.0 to about 8.0.

Additional advantages of the disclosure will be set forth in part in the description which follows or may be learned by practice of the disclosure. The advantages will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure, as claimed.

DESCRIPTION OF THE EMBODIMENTS

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein are to be understood to encompass any and all sub-ranges subsumed therein. For example, a range of “less than 10” can include any and all sub-ranges between (and including) the minimum valve of zero and the maximum valve of 10, that is, any and all sub-ranges having a minimum valve of equal to or greater than zero and a maximum value of equal to or less than 10, e.g., 1 to 5.

The lubricant composition of the present disclosure can comprise a major amount of a base oil, and a minor amount of an additive composition comprising an overbased detergent and a low-base detergent, wherein the lubricant composition has a salt to metal ratio ranging from about 3.0 to about 8.0. As used herein, the term “major amount” is understood to mean an amount greater than or equal to 50 wt. %, for example from about 80 to about 98 wt. % relative to the total weight of the lubricant composition. Moreover, as used herein, the term “minor amount” is understood to mean an amount less than 50 wt. % relative to the total weight of the lubricant composition.

The disclosed lubricant composition and the additive composition can be formulated for a variety of uses such as, for example, crankcase lubricant composition for spark ignition and compression-ignition internal combustion engines, including automobile and truck engines, two cycle engines, aviation piston engines, marine, and low load diesel engines, rotary engines, hybrid engines, and the like.

Base oils suitable for use in formulating the disclosed compositions can be selected from any of the synthetic or mineral oils or mixtures thereof. Mineral oils include animal oils and vegetable oils (e.g., castor oil, lard oil) as well as other mineral lubricating oils such as liquid petroleum oils and solvent treated or acid-treated mineral lubricating oils of the paraffinic, naphthenic or mixed paraffinic-naphthenic types. Oils derived from coal or shale can also suitable. Further, oils derived from a gas-to-liquid process can also suitable.

The base oil typically can have a viscosity of, for example, from about 2 to about 15 cSt and, as a further example, from about 2 to about 10 cSt at 100° C. Thus, the base oils can normally have a viscosity in the range of about SAE 50 to about SAE 250, and more usually can range from about SAE 70W to about SAE 140. Suitable automotive oils also include cross-grades such as 75W-140, 80W-90, 85W-140, 85W-90, and the like.

Non-limiting examples of synthetic oils include hydrocarbon oils such as polymerized and interpolymerized olefins (e.g., polybutylenes, polypropylenes, propylene isobutylene copolymers, etc.); polyalphaolefins (e.g. poly(1-hexenes), poly-(1-octenes, poly(1-decenes), etc., and mixtures thereof); alkylbenzenes (e.g., dodecylbenzenes, tetradecylbenzenes, di-nonylbenzenes, di-(2-ethylhexyl)benzenes, etc.); polyphenyls (e.g., biphenyls, terpenyl, alkylated polyphenyls, etc.); alkylated diphenyl ethers and alkylated diphenyl sulfides and the derivatives, analogs and homologs thereof and the like.

Alkylene oxide polymers and interpolymers and derivatives thereof where the terminal hydroxyl groups have been modified by esterification, etherification, etc., constitute another class of known synthetic oils that can be used. Such oils can be exemplified by the oils prepared through polymerization of ethylene oxide or propylene oxide, the alkyl and aryl ethers of these polyoxyalkylene polymers (e.g., methyl-polyisopropylene glycol ether having an average molecular weight of about 1000, diphenyl ether of polyethylene glycol having a molecular weight of about 500-1000, diethyl ether of polypropylene glycol having a molecular weight of about 1000-1500, etc.) or mono- and polycarboxylic esters thereof, for example, the acetic acid esters, mixed C₃₋₈ fatty acid esters, or the C₁₃ oxo acid diester of tetraethylene glycol.

Another class of synthetic oils that can be used includes the esters of dicarboxylic acids (e.g., phthalic acid, succinic acid, alkyl succinic acids, alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebacic acid, fumaric acid, adipic acid, linoleic acid dimer, malonic acid, alkyl malonic acids, alkenyl malonic acids, etc.) with a variety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2- ethylhexyl alcohol, ethylene glycol, diethylene glycol monoether, propylene glycol, etc.). Specific examples of these esters include dibutyl adipate, di(2-ethylhexyl)sebacate, di-n-hexyl fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate, didecyl phthalate, dieicosyl sebacate, the 2- ethylhexyl diester or linoleic acid dimer, the complex ester formed by reacting one mole of sebacic acid with two moles of tetraethylene glycol and two moles of 2-ethylhexanoic acid and the like.

Esters useful as synthetic oils also include those made from C5-12 monocarboxylic acids and polyols and polyol ethers such as neopentyl glycol, trimethylol propane, pentaerythritol, dipentaerythritol, tripentaerythritol, etc.

Hence, the base oil which can be used to make the compositions as described herein can be selected from any of the base oils in Groups I-V as specified in the American Petroleum Institute (API) Base Oil Interchangeability Guidelines. Such base oil groups are as follows:

Group I contain less than 90% saturates and/or greater than 0.03% sulfur and have a viscosity index greater than or equal to 80 and less than 120; Group II contain greater than or equal to 90% saturates and less than or equal to 0.03% sulfur and have a viscosity index greater than or equal to 80 and less than 120; Group III contain greater than or equal to 90% saturates and less than or equal to 0.03% sulfur and have a viscosity index greater than or equal to 120; Group IV are polyalphaolefins (PAO); and Group V include all other basestocks not included in Group I, II, III or IV.

The test methods used in defining the above groups are ASTM D2007 for saturates; ASTM D2270 for viscosity index; and one of ASTM D2622, 4294, 4927 and 3120 for sulfur.

Group IV basestocks, i.e. polyalphaolefins (PAO) include hydrogenated oligomers of an alpha-olefin, the most important methods of oligomerisation being free radical processes, Ziegler catalysis, and cationic, Friedel-Crafts catalysis.

The polyalphaolefins typically have viscosities in the range of about 2 to about 100 cSt at 100° C., for example about 4 to about 8 cSt at 100° C. They can, for example, be oligomers of branched or straight chain alpha-olefins having from about 2 to about 30 carbon atoms, non-limiting examples include polypropylenes, polyisobutenes, poly-1-butenes, poly-1-hexenes, poly-1-octenes and poly-1-decene, included are homopolymers, interpolymers and mixtures.

Regarding the balance of the basestock referred to above, a “Group I basestock” also includes a Group I basestock with which basestock(s) from one or more other groups can be admixed, provided that the resulting admixture has characteristics falling within those specified above the Group I basestocks.

Exemplary basestocks include Group I basestocks and mixtures of Group II basestocks with Group I base stocks.

Basestocks suitable for use herein can be made using a variety of different processes including but not limited to distillation, solvent refining, hydrogen processing, oligomerisation, esterification, and re-refining.

The base oil can be an oil derived from Fisher-Tropsch synthesized hydrocarbons. Fischer-Tropsch synthesized hydrocarbons can be made from synthesis gas containing H₂ and CO using a Fischer-Tropsch catalyst. Such hydrocarbons typically require further processing in order to be useful as the base oil. For example, the hydrocarbons can be hydroisomerized using processes disclosed in U.S. Pat. Nos. 6,103,088 or 6,180,575; hydrocracked and hydroisomerized using processes disclosed in U.S. Pat Nos. 4,943,672 or 6,096,940; dewaxed using processes disclosed in U.S. Pat. No. 5,882,505; or hydroisomerized and dewaxed using processes disclosed in U.S. Pat. Nos. 6,013,171; 6,080,301; or 6,166,949.

Unrefined, refined and rerefined oils, either mineral or synthetic (as well as mixtures of two or more of any of these) of the type disclosed hereinabove can be used in the base oils. Unrefined oils are those obtained directly from a mineral or synthetic source without further purification treatment. For example, a shale oil obtained directly from retorting operations, a petroleum oil obtained directly from primary distillation or ester oil obtained directly from an esterification process and used without further treatment would be an unrefined oil. Refined oils are similar to the unrefined oils except they have been further treated in one or more purification steps to improve one or more properties. Many such purification techniques are known to those skilled in the art such as solvent extraction, secondary distillation, acid or base extraction, filtration, percolation, etc. Rerefined oils are obtained by processes similar to those used to obtain refined oils applied to refined oils which have been already used in service. Such rerefined oils are also known as reclaimed or reprocessed oils and often are additionally processed by techniques directed to removal of spent additives, contaminants, and oil breakdown products.

Detergents can be present in the disclosed compositions to keep an insoluble material in suspension and can prevent its deposition where it could be harmful. Detergents can also redisperse deposits already formed. Detergents can typically possess acid-neutralizing properties. The lubricant and additive compositions disclosed herein can comprise at least one detergent. In an aspect, the lubricant and additive compositions can comprise at least two detergents, one of which can be an overbased detergent, the other of which can be a low-base detergent.

The detergents used herein can be any detergent. Non-limit examples of detergents include sulfonates, phenates, sulfurized phenates, carboxylates, salicylates, thiophosphonates, naphthenates of a metal, particularly or alkali or alkaline earth metals, for example barium, sodium, potassium, lithium, calcium, and magnesium and combinations thereof.

In general, the detergents can comprise a polar head with a long hydrophobic tail, with the polar head comprising a metal salt of an organic acid. The salts can comprise a substantially stoichiometric amount of the metal. The total base number (TBN) of a detergent is the amount of acid needed to neutralize all of the alkalinity of the material, and can be determined according to ASTM D 2896. As an example, an overbased detergent with a TBN of 150 or greater can be prepared by reacting an acidic material (typically an inorganic acid or lower carboxylic acid, such as carbon dioxide) with a mixture comprising an acidic organic compound and a stoichiometric excess of metal base.

A low-base detergent that can be used in the disclosed lubricant composition can have a TBN of about 150 or less, for example less than about 80, as a further example less than 50, and as another example less than about 30.

the low-base detergent can be present in the disclosed lubricant composition in any desired or effective amount. In an aspect, the low-base detergent can be present in the lubricant composition in an amount ranging from about 0.1 wt. % to about 3.5 wt. %, for example from about 0.5 wt. % to about 3 wt. %, and as a further example from about 1.0 wt. % to about 3 wt. % relative to the total weight percent of the lubricant composition. The low-base detergent can have a metal content ranging from about 0.005 wt. % to about 0.175 wt. %, for example from about 0.025 wt. % to about 0.15 wt. %, and as a further example from about 0.075 wt. % to about 0.15 wt. % relative to the total weight percent of the low-based detergent.

The overbased detergent for use in the disclosed lubricant composition can have a TBN of greater than about 150, for example greater than about 250, and as a further example greater than about 400. In an aspect, the TBN can range from about 150 to about 500.

The overbased detergent can be present in the disclosed lubricant composition in any desired or effective amount. In an aspect, the overbased detergent can be present in an amount ranging from about 0.5 wt. % to about 3.5 wt. %, for example from about 1 wt. % to about 2.5 wt. % relative to the total weight of the lubricant composition. The overbased detergent can have a metal content ranging from about 0.05 wt. % to about 0.7 wt. %, and for example from about 0.1 wt. % to about 0.5 wt. % relative to the total weight percent of the overbased detergent.

In various aspects, the disclosed lubricant composition can have a weight ratio of the low-base detergent to the overbased detergent in the range of about 0.1 to about 7, for example from about 0.2 to about 5, and as a further example from about 0.5 to about 2.5.

In some aspects, the disclosed lubricant composition can have a salt to metal ratio ranging from about 3.0 to about 8.0, for example from about 3.5 to about 7.5, and as a further example from about 4.0 to about 6.5.

Non-limiting examples of suitable metal-containing detergents include, but are not limited to, salts and overbased salts of such substances as lithium phenates, sodium phenates, potassium phenates, calcium phenates, magnesium phenates, barium phenates, sulfurized lithium phenates, sulfurized barium phenates, sulfurized sodium phenates, sulfurized potassium phenates, sulfurized calcium phenates, and sulfurized magnesium phenates wherein each aromatic group has one or more aliphatic groups to impart hydrocarbon solubility; lithium sulfonates, barium sulfonates, sodium sulfonates, potassium sulfonates, calcium sulfonates, and magnesium sulfonates wherein each sulfonic acid moiety is attached to an aromatic nucleus which in turn usually contains one or more aliphatic substituents to impart hydrocarbon solubility; lithium salicylates, barium salicylates, sodium salicylates, potassium salicylates, calcium salicylates, and magnesium salicylates wherein the aromatic moiety is usually substituted by one or more aliphatic substituents to impart hydrocarbon solubility; the lithium, sodium, barium, potassium, calcium and magnesium salts of hydrolysed phosphosulfurized olefins having 10 to 2,000 carbon atoms or of hydrolyzed phosphosulfurized alcohols, and/or aliphatic-substituted phenolic compounds having 10 to 2,000 carbon atoms, lithium, sodium, barium, potassium, calcium and magnesium salts of aliphatic carboxylic acids and aliphatic-substituted cycloaliphatic carboxylic acids; and many other similar alkali and alkaline earth metal salts of oil-soluble organic acids. Mixtures of overbased salts of two or more different alkali and/or alkaline earth metals can be used. Likewise, overbased salts of mixtures of two or more different acids or two or more different types of acids (e.g., one or more overbased calcium phenates with one or more overbased calcium sulfonates) can also be used.

Methods for the production of overbased alkali and alkaline earth metal-containing detergents are well known to those skilled in the art and are extensively reported in the patent literature. See for example, the disclosures of U.S. Pat. Nos. 2,451,345; 2,451,346; 2,485,861; 2,501,731; 2,501,732; 2,585,520; 2,671,758; 2,616,904; 2,616,905; 2,616,906; 2,616,911; 2,616,924; 2,616,925; 2,617,049; 2,695,910; 3,178,368; 3,367,867; 3,488,284; 3,496,105; 3,629,109; 3,779,920; 3,865,737; 3,907,691; 4,100,085; 4,129,589; 4,137,184; 4,148,740; 4,212,752; 4,394,277; 4,563,293; 4,617,315; 4,647,387; 4,880,550; 5,075,383; 5,139,688; 5,238,588; 5,652,201; 6,107,257; 6,444,625; 6,869,919; and 6,423,670; GB Published Patent Application 2,082,619 A; and European Patent Application Publication Nos. 121,024 B1 and 259,974 A2, the disclosures of which are incorporated herein by reference.

The lubricant composition of the present disclosure can also include “hybrid” detergents formed with mixed surfactant systems, e.g., phenate/salicylates, sulfonate/phenates, sulfonate/salicylates, sulfontates/phenates/salicylates, as described, for example, in U.S. Pat. Nos. 6,153,565; 6,281,179; 6,429,178; 6,429,179; and 6,869,919.

Another class of detergents that can be used in the lubricant composition of the present disclosure includes zinc detergents such as, for example, zinc sulfonates, zinc carboxylates, zinc salicylates, zinc phenates and sulfurized zinc phenates and mixtures thereof as disclosed in U.S. Pat. No. 6,482,778, which is herein incorporated by reference. Overbased zinc detergents can be formed by reaction between a neutral zinc detergent and a metal hydroxide. This reaction typically can takes place using carbon dioxide in the presence of a promoter, which is generally an alcohol-type material. The promoter dissolves a small amount of metal hydroxide, which is subsequently reacted with carbon dioxide to form a metal carbonate. The amount of metal carbonate incorporated into the overbased detergents can vary depending upon the application in which the overbased detergent is used. Zinc sulfonates such as, for example, including but not limited to zinc dihydrocarbyl aromatic sulfonates such as zinc dialkylnaphthalene sulfonate can also be used in the lubricant composition of the present disclosure. The zinc dialkylnaphthalene sulfonate has a sulfonate group attached to one ring of the naphthalene nucleus and an alkyl group attached to each ring. Each alkyl group can independently contain from about six to about twenty carbon atoms, but they can contain from about eight to twelve carbon atoms. The dialkylnaphthalene sulfonate group is attached to the zinc through the sulfonate group.

The lubricant composition can further comprise other optional additives such as dispersants, anti-wears, antioxidants, antifoamers, diluents, friciton modifiers, viscosity index improvers, pour-point depressants, etc. These optional additives can be present in any desired effective amount so long as they do not interfere with the disclosed detergents.

According to various embodiments, there is a method of improving piston cleanliness. As used herein, the term “improving piston cleanliness” is understood to mean enhancing the cleanliness of the piston, e.g., reducing the amount of deposits on the piston, as compared to a piston that has not been provided with the disclosed lubricant composition. The method of improving piston cleanliness can comprise providing to at least one piston a lubricant composition comprising a major amount of a base oil and a minor amount of an additive composition comprising an overbased detergent and a low-base detergent, wherein the lubricant composition has a salt to metal ratio ranging from about 3.0 to about 8.0.

In other embodiments, there is a method of passing a Sequence IIIG test in a combustion system. The method can comprise providing to the combustion system, a lubricant composition including a major amount of a base oil and a minor amount of an additive composition, wherein the additive composition can comprise an overbased detergent and a low-base detergent, wherein the lubricant composition has a salt to metal ratio ranging from about 3.0 to about 8.0.

By “combustion system” herein is meant, for example and not by limitation herein, any diesel-electric hybrid vehicle, a gasoline-electric hybrid vehicle, a two-stroke engine, any and all burners or combustion units, including for example and without limitation herein, stationary burners (home heating, industrial, boilers, furnaces), waste incinerators, diesel fuel burners, diesel fuel engines (unit injected and common rail), jet engines, HCCI engines automotive diesel engines, gasoline fuel burners, gasoline fuel engines (PFI and DIG), power plant generators, and the like. The hydrocarbonaceous fuel combustion systems that may benefit from the present disclosure include all combustion units, systems, devices, and/or engines that burn fuels. By “combustion system” herein is also meant any and all internal and external combustion devices, machines, engines, turbine engines, jet engines, boilers, incinerators, evaporative burners, plasma burner systems, plasma arc, stationary burners, and the like which can combust or in which can be combusted a hydrocarbonaceous fuel.

According to various embodiments, there is method of lubricating moving parts of a machine, said method comprising contacting at least one moving part with a lubricant composition comprising a major amount of a base oil and a minor amount of an additive composition comprising an overbased detergent and a low-base detergent, wherein the lubricant composition has a salt to metal ratio ranging from about 3.0 to about 8.0. In some embodiments, the machine in the method of lubricating moving parts can be selected from the group consisting of spark ignition and compression-ignition internal combustion engines, including automobile and truck engines, gas engines, diesel engines, turbine engines, aviation piston engines, marine engines, rotary engines, and hybrid engines.

EXAMPLE

Three different lubricant compositions: A, B, and C were formulated as shown in Table 1. A and B were formulated with similar dispersant/detergent inhibitor (DI) systems, but with different mixtures of base fluids. B and C were formulated with similar base fluids, but with different ratios of overbased detergent to low-base detergent.

TABLE 1 A B C 5W-30 5W-30 5W-30 Dispersant #1 1.5 1.5 1.5 #2 3.2 3.2 3.2 Detergent #1 Overbased Ca sulfonate 1.6 1.6 1.4 (TBN 307, 25% neutral salt) (0.19 wt. % Ca) (0.19 wt. % Ca) (0.17 wt. % Ca) #2 Low-base Ca sulfonate 0.5 0.5 2.5 (TBN 28, 40% neutral salt) (0.013 wt. % Ca) (0.013 wt. % Ca) (0.065 wt. % Ca) Anti-wear ZDDP 0.85 0.85 0.85 Antioxidant #1 0.5 0.5 0.5 #2 — 1.0 1.0 #3 1.0 — — #4 0.3 0.3 0.3 Antifoamer 0.006 0.006 0.006 Diluent Oil 0.594 0.594 0.594 Friction 0.35 0.35 0.35 Modifier Viscosity index 8.0 8.0 7.8 improver Pour-Point 0.1 0.1 0.1 Depressant Base Oil #1 Group III 10.0 — — #2 Group III — 26.6 34.9 #3 Group V — 15.0 5.0 #4 Group IV 33.0 40.0 40.0 #5 Group I 16.5 — — #6 Group I 22.0 — — Total 100.0 100.0 100.0

Table 2 provides the elemental analysis of the three formulations.

TABLE 2 A B C Analytical Data 5W-30 5W-30 5W-30 Phosphorus wt. % 0.068 0.068 0.068 Zinc wt. % 0.078 0.078 0.078 Calcium wt. % 0.20 0.20 0.24 Salt-to-Metal Ratio 2.95 2.95 5.83

The three formulations, A, B, and C as described in Table 1 were subjected to the Sequence IIIG test to measure oil thickness and piston deposits under high temperature conditions and to provide information about valve train wear. Table 3 show the results of the Sequence IIIG tests.

TABLE 3 Sequence IIIG A B C Test Limit for GM4718M 5W-30 5W-30 5W-30 100 hour Viscosity Increase 90% maximum 53.4 28.1 27.6 Weighted Piston Deposit 5.5 Minimum 4.10 4.56 5.76 Average Camshaft and 60 μm 18.8 16.2 15.8 Lifter Wear Maximum Oil Consumption L 2.71 2.06 2.23

As can be seen from Table 3, A and B passed the Sequence IIIG requirements for GF-4/SM, but failed to meet the more stringent WPD performance (WPD at 5.5 minimum) for GM4718M. Further it is to be noticed that C performed better than B with respect to the WPD. Because B and C were formulated with basically the same mixture of base fluids, but with different ratios of overbased detergent to low-base detergent, the better performance of C can be attributed to the different mixture of overbased and low-base detergent. Table 2 further shows elemental analysis of the three formulations A, B, and C. It should be noted that while A and B have the same ratio of salt to metal, C has a higher value.

At numerous places throughout this specification, reference has been made to a number of U.S. patents, published foreign patent applications and published technical papers. All such cited documents are expressly incorporated in full into this disclosure as if fully set forth herein.

For the purposes of this specification and appended claims, unless otherwise indicated, all numbers expressing quantities, percentages or proportions, and other numerical values used in the specification and claims, are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

It is noted that, as used in this specification and the appended claims, the singular forms “a,” “an, ” and “the,” include plural referents unless expressly and unequivocally limited to one referent. Thus, for example, reference to “an antioxidant” includes one or more different antioxidants. As used herein, the term “include” and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items.

This invention is susceptible to considerable variation in its practice. Therefore the foregoing description is not intended to limit, and should not be construed as limiting, the invention to the particular exemplifications presented hereinabove. Rather, what is intended to be covered is as set forth in the ensuing claims and the equivalents thereof permitted as a matter of law.

Applicant does not intend to dedicate any disclosed embodiments to the public, and to the extent any disclosed modifications or alterations may not literally fall within the scope of the claims, they are considered to be part of the invention under the doctrine of equivalents. 

1. A lubricant composition comprising: a major amount of a base oil; and a minor amount of an additive composition comprising an overbased detergent and a low-base detergent, wherein the lubricant composition has a salt to metal ratio ranging from about 3.0 to about 8.0.
 2. The lubricant composition of claim 1, wherein the overbased detergent and low-base detergent are selected from the group consisting of sulfonates, phenates, sulfurized phenates, carboxylates, salicylates, thiophosphonates, naphthenates of a metal, and combinations thereof.
 3. The lubricant composition of claim 1, wherein the overbased detergent is present in an amount ranging from about 0.5 wt. % to about 3.5 wt. %, relative to the total weight of the composition.
 4. The lubricant composition of claim 1, wherein the overbased detergent has a total base number greater than about
 150. 5. The lubricant composition of claim 4, wherein the overbased detergent has a total base number greater than about
 250. 6. The lubricant composition of claim 1, wherein the overbased detergent has a metal content ranging from about 0.05 wt. % to about 0.7 wt. %.
 7. The lubricant composition of claim 6, wherein the overbased detergent has a metal content ranging from about 0.1 wt. % to about 0.5 wt. %.
 8. The lubricant composition of claim 1, wherein the weight ratio of the low-base detergent to the overbased detergent ranges from about 0.1 to about
 7. 9. The lubricant composition of claim 1, wherein the low-base detergent is present in an amount ranging from about 0.1 wt. % to about 3.5 wt. % relative to the total weight of the composition.
 10. The lubricant composition of claim 1, wherein the low-base detergent has a total base number of about 150 or less.
 11. The lubricant composition of claim 10, wherein the low-base detergent has a total base number less than about
 80. 12. The lubricant composition of claim 1, wherein the low-base detergent has a metal content ranging from about 0.005 wt. % to about 0.175 wt. %.
 13. The lubricant composition of claim 6, wherein the low-base detergent has a metal content ranging from about 0.025 wt. % to about 0.15 wt. %.
 14. The lubricant composition of claim 1, wherein the lubricant composition has a salt to metal ratio ranging from about 3.5 to about 7.5.
 15. The lubricant composition of claim 1, wherein the lubricant composition has a salt to metal ratio ranging from about 4.0 to about 6.5.
 16. The lubricant composition of claim 1, further comprising at least one additive selected from the group consisting of dispersants, anti-wears, antioxidants, friction modifiers, anti-foamers, diluents, pour-point depressants, and viscosity index improvers.
 17. A method of improving piston cleanliness comprising: providing to at least one piston a lubricant composition comprising a major amount of a base oil; and a minor amount of an additive composition comprising an overbased detergent and a low-base detergent, wherein the lubricant composition has a salt to metal ratio ranging from about 3.0 to about 8.0.
 18. A method of passing a Sequence IIIG test in a combustion system comprising: providing to the combustion system a lubricant composition comprising a major amount of a base oil; and a minor amount of an additive composition comprising an overbased detergent and a low-base detergent, wherein the lubricant composition has a salt to metal ratio ranging from about 3.0 to about 8.0.
 19. A method of passing a Sequence IIIG test in a combustion system comprising: providing to the combustion system a lubricant composition comprising a major amount of a base oil; and a minor amount of an additive composition comprising an overbased detergent and a low-base detergent, wherein the lubricant composition has a salt to metal ratio ranging from about 3.0 to about 8.0.
 20. The method of claim 19, wherein the machine is selected from the group consisting of spark ignition and compression-ignition internal combustion engines. 